10 Ways Insects Defend Themselves

Toxic Sprays, Clever Disguises, and Other Ways Bugs Protect Themselves

Warbler eating insects.
How do insects defend themselves against hungry predators?. Getty Images/Glenn Bartley

It's a bug-eat-bug world out there. It's also a bird-eat-bug world, a frog-eat-bug world, a lizard-eat-bug world, and a, well, you get the picture. Almost anything that's bigger than an insect will try to eat said insect. And so, what can an insect do to survive?

Insects have thrived on our planet for hundreds of millions of years, so they must be doing something right despite all the threats to their survival. They may be small, but they've come up with all kinds of ways to keep from being eaten. From caustic sprays to venomous stings, and everything in between, let's take a look at 10 ways insects defend themselves.

01
of 10

Put Up a Stink

Black swallowtail caterpillar.
Some swallowtail caterpillars defend themselves by releasing foul-smelling toxins from a special gland called an osmeterium (the Y-shaped orange structure). Getty Images/by Grant and Caroline

Sometimes, all it takes to discourage a potential predator is a foul smell. Would you want to eat something that smells terrible? 

Repellant Odors

Many insects use repellant odors to protect themselves, and perhaps the best known group of such insects is the stink bugs. A stink bug has a special reservoir for storing a small amount of foul-smelling hydrocarbons, which the bug produces via specialized glands. The vile substance is released any time the stink bug feels threatened.

Some swallowtail caterpillars make quite a show of releasing their repellant compounds. These caterpillars concentrate toxins from their food plants and store them in a special thoracic pouch. When touched, the swallowtail caterpillar everts a Y-shaped gland, called an osmeterium, and waves it in the air, releasing the stinky and toxic substance for all to whiff.

02
of 10

Spray Them With Irritants

Blister beetle.
Blister beetles reflex bleed when handled, releasing a blistering agent called cantharidin. Handle them with care. Getty Images/Matt Meadows

Some clever insects distract predators by oozing or spraying irritating substances on them. When the predator reacts, usually stopping to clean itself off, the insect makes a clean getaway.

Irritating Substances

Insects that use defensive chemicals to protect themselves often practice an adaptation known as reflex bleeding, exuding hemolymph from their leg joints. Ladybugs are known to exhibit this behavior, for example. Blister beetles also reflex bleed, releasing a blistering agent called cantharidin, which can seriously irritate your skin. Handle blister beetles with care (or better yet, forceps!).

Bombardier beetles famously spray predators with a mixture of chemicals, and can do so with impressive force. The beetle stores the ingredients for this caustic compound separately in special abdominal chambers. When threatened, it quickly mixes them together and shoots a jet of irritants in the direction of the perceived predator.

03
of 10

Stab Them With Spines

Saddleback caterpillar.
Beware of caterpillars with bristles or hairs! They often sting. Getty Images/Danita Delimont

Some insects use poison-filled hairs to get under a predator's skin (literally).

Urticating Hairs

A handful of caterpillars use special toxic hairs to discourage predators. Called urticating hairs, these hollow setae are each attached to a special glandular cell that pumps poison into it. All you have to do is brush your finger against the caterpillar, and you'll feel the effects as the hairs break and release toxins into your skin. The pain is often described as feeling like you have tiny bits of fiberglass embedded in your finger.

While some stinging caterpillars look rather threatening, with stiff branched spines, others, like the puss moth caterpillar, appear furry and invite a touch. A good rule of thumb (or finger) is to avoid touching any caterpillar that appears prickly or furry.

04
of 10

Sting Them

Hornet nest and flying hornets.
Bees and wasps will defend their nests vigorously by stinging perceived threats. Getty Images/Premium/UIG

 Then there's the more direct approach to inflicting pain – stinging.

Envenomation

Many bees, wasps, and even ants will go on the offensive when threatened. Social bees are particularly protective of their nests, and may defend their home en masse. They use a modified ovipositor, or sting, to inject venom directly into the potential predator. The venom usually causes enough pain to send the predator packing, and when multiple insects sting a single victim, it can even be life threatening. Venom allergies can also be deadly. So despite their diminutive size, stinging bees, wasps, and ants are fully capable of defending themselves from harm.

05
of 10

Blend Into the Background

A moth camouflaged against tree bark.
Can you find the moth? This one blends perfectly into the tree bark. Getty Images/John Macgregor

Some insects are masters of disguise, making it all but impossible for predators to find them.

Crypsis or Camouflage

You can't be eaten if the predator can't see you. That's the principle behind crypsis or cryptic coloration, the art of blending into your habitat. Have you ever tried to find a mottled brown and green grasshopper in a meadow? Good luck! There are butterflies the exact color of leaves, moths that blend into bark, and lacewings that up their camouflage game by covering themselves in bits of lichen or moss.

The one big disadvantage of cryptic coloration is that the insect has to stay put for it to work. If the leaf insect wanders off the plant, for example, it's camouflage won't protect it.

06
of 10

Hide in Plain Sight

Giant swallowtail caterpillar.
Bird dropping? Ick! Take a closer look – that's actually a caterpillar. Getty Images/C. Allan Morgan

Some insects take the art of camouflage to the next level, and look so much like objects from their environment, they can hide in plain sight without fear of being spotted.

Mimesis

Stick and leaf insects are the best examples of insects that use this defensive strategy. Leaf insects mimic the shape, color, and even vein patterns in the leaves of the plants where they live. Stick insects can even have bumps and knots that mirror those on twigs where they perch, and if you watch them, you'll see them purposefully sway and rock in the breeze like a twig. 

And then there are the bird dropping caterpillars. Did you know there are caterpillars made to look like bird poop? This particular form of camouflage is found in the swallowtails, and enables early instar caterpillars to remain in the open without being eaten. What predator is going to taste something that looks like a bird dropping?

07
of 10

Wear a Warning

Shield bug.
This shield bug, with its bright red and black stripes, is warning predators to stay away. Getty Images/David Courtenay

Unpalatable insects don't want predators to nibble them before deciding they aren't a worthwhile treat, so they advertise their unappealing taste with bright colors.

Aposematic Coloration

Aposematic coloration is a way for insects and other animals to warn predators away without making the ultimate sacrifice. The term aposematic comes from the Greek words apo, which means distant, and sema, meaning sign. 

Common aposematic color patterns are red and black (think lady beetles and milkweed bugs), orange and black (think monarch butterflies), and yellow and black (think bees and wasps). Brightly colored insects are usually advertising their unappetizing taste, and sometimes their toxicity as a food for predators.

Of course, the predator has to learn to associate the bright colors with a disappointing meal, so a few insects will be sacrificed until the bird or reptile gets the message. But aposematic coloration is for the greater good of the insect community!

08
of 10

Disguise Yourself As Something Scary

Hover fly.
Hover flies are convincing bee mimics. Getty Images/Heino Klinnert/EyeEm

Of course, if you don't happen to be an unpalatable insect, you can use false advertising to your advantage.

Mimicry

Warning colors used by unsavory insects work so well, perfectly tasty and non-toxic insects have taken to disguising themselves as insects that predators know to avoid. The most classic example of this mimicry, a defensive adaptation described by Henry Bates, is the viceroy butterfly. Viceroys aren't toxic at all, but they look suspiciously similar to the monarch butterfly, a species that predators will avoid.

All kinds of insects use this strategy to their benefit, and many of these are bee mimics. Clear-winged sphinx moths look like large bumblebees, and complete their disguise by visiting flowers during the day. Many flies, including drone flies and hover flies, look striking similarly to bees or wasps, so much so that they're often misidentified as such.

09
of 10

Let Go of a Leg

Walkingstick.
A walkingstick will shed a leg to avoid being captured by a predator. Getty Images/Panoramic Images

For some insects, the best means of survival is to give up a body part to a predator. 

Autotomy

Did you see the movie 127 Hours, which was the true story of a hiker who sawed off his own hand to save himself when his arm was pinned down by a boulder? Many insects make that choice, too, only it's much less gruesome for arthropods. 

Certain insects are well-prepared to sacrifice a leg for the good of the body. They've actually got built-in fracture lines at certain joints in their legs, which allows the leg to break cleanly when in the grip of a predator. This limb shedding adaptation, called autotomy, is most common in long-legged insects like walking sticks, craneflies, and katydids. If the loss of a leg occurs when the walking stick is young, it may even regenerate the limb over the course of several molts.

10
of 10

Play Dead

Lady beetle on its back.
Lady beetles play dead, a practice called thanatosis, to avoid predation. Getty Images/mikroman6

Sometimes, the easiest way for an insect to protect itself from a threat is simply to stop, drop, and roll.

Thanatosis

Playing opossum isn't just for, well, opossums. Did you know insects play dead, too? This behavior is called thanatosis, and it's surprisingly common among arthropods. Certain tiger moth caterpillars, for example, will quickly curl themselves into a ball when you touch them, and they'll stay that way until the threat has passed. Millipedes are also known for coiling themselves up and staying still to avoid danger.

If you've ever tried to snag a beetle from a leaf, you've probably seen a demonstration of thanatosis in action. Lady beetles, leaf beetles, and other skittish insects will simply loosen their grip on the plant in question, fall to the ground, and lie there looking dead until you leave them be. There's even a genus of beetles (Cryptoglossa, if you're curious) known as death-feigning beetles.

Sources:

  • Evolution and Adaptation of Terrestrial Arthropods, by John L. Cloudsley-Thompson

  • The Insects: An Outline of Entomology, by P. J. Gullan and P. S. Cranston

  • "Insect Defenses," by John R. Meyer, North Carolina State University Department of Entomology website. Accessed online July 21, 2016.

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Hadley, Debbie. "10 Ways Insects Defend Themselves." ThoughtCo, Nov. 16, 2017, thoughtco.com/ways-insects-defend-themselves-4065571. Hadley, Debbie. (2017, November 16). 10 Ways Insects Defend Themselves. Retrieved from https://www.thoughtco.com/ways-insects-defend-themselves-4065571 Hadley, Debbie. "10 Ways Insects Defend Themselves." ThoughtCo. https://www.thoughtco.com/ways-insects-defend-themselves-4065571 (accessed January 21, 2018).